New data on November eruption

The eruption of Ardoukoba began on 7 November. During the preceding 24 hours, about 800 earthquakes M < 3.3 had been recorded. These events occurred at the end of the Ghoubbat al Kharab (figure 2), just S of the rift and ~6 km SE of the eruption site.

Figure 2. Rock types, faults, and old volcanic cones in the Ardoukoba Rift, after Needham and others (1976). An overprint, from M. Krafft, shows the active vents and lava flows from the 7-14 November 1978 eruption and the zone of active faulting accompanying the eruption.

After a brief period of gas emission, lava fountaining began from a 500-m-long, newly opened fissure. Three spatter cones formed on this fissure, but the primary activity soon shifted about 1/2 km to the SE. For the first 2-4 hours as much as 0.5 x 10⁶ m³ of lava was extruded per hour, but the extrusion rate declined rapidly and by the 5th or 6th day had decreased by an order of magnitude.

By 9 November, only the main vent was still active. A cone (named Gira-le-Koma) about 30 m high, 200 m long, and 25 m wide, with a 60° external slope, had formed around this vent, which contained a small lava lake. On 13 November the level of the lava lake dropped rapidly, then the lake disappeared. Scoria and bombs were ejected briefly before the eruption ended on 14 November.

The total volume of lava emitted was estimated to be at least 12 x 10⁶ m³. Lava covered an area of slightly more than 3 km². Flow thicknesses reached 25 m but usually ranged from 1 to 2 m. About 25 fissures, parallel to the NW-SE trend of the rift, opened during the activity. Most fissures were from 1-2 mm to about 1 m wide, but there was one short segment of 3 m width. Many of the fissures also showed a component of normal movement, with scarps up to 1/2 m high.

Reference. Needham and others, 1976, The accreting plate boundary: Ardoukoba Rift (northeast Africa) and the oceanic rift system: Earth and Planetary Science Letters, v. 28, p 439-453.

Further References. Abdallah, A., and others, 1979, Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries: Nature, v. 282, p. 17-23.

Demange, J., and Tazieff, H., 1978, The "tectonic" eruption of the Ardoukoba (Djibouti): C.R. Acad. Sci. Paris, Ser. D, v. 287, p. 1269-1272.

Hernandez, J., and Ruegg, J.C., eds., 1980, Colloque Rift d'Asal: Réunion extraordinaire de la Société Géologique de France: Bulletin de la Societé Géologique de France, serie 7, t. XXII, no. 6, p. 797-1013.

Tarantola, A., Ruegg, J.C., and Lepine, J.C., 1979, Geodetic evidence for rifting in Afar: A brittle-elastic model for the behavior of the lithosphere: Earth and Planetary Science Letters, v. 45, p. 435-444.

Information Contacts: M. Krafft, Cernay.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

November 1978 (SEAN 03:11) Cite this Report

Basaltic lava flows; first eruption in as much as 3,000 years

The crew of a French observation aircraft saw an eruption early 8 November in a virtually uninhabited area SE of Lake Assal. On the preceding day a series of weak earthquakes was felt in the city of Djibouti and two larger shallow events were located by the U. S. Geological Survey's National Earthquake Information Center (USGS/NEIC). The first, mb 5.2, occurred on 7 November at 2006 (felt as a sharp shock in Djibouti) and the second, mb 5.0, on 8 November at 0808. Hypocenters calculated by the USGS for these events are 8 and 17 km WSW of the eruption, or well within the location error for events in this region.

Two basaltic lava flows were reportedly extruded: one flow traveled ~1 km to the SE, the other ~0.5 km to the NW. Lava effusion rates reached an estimated maximum of 1,000 m³/minute [but see 0.5 x 10⁶ m³/hour below]. Ash clouds rose ~300 m and larger pyroclastics ~70 m. The eruption formed a crater ~30 m in diameter and built a cone ~100 m high.

Activity began to decline 14 November and within two days only steaming was visible. As of 22 November, some vapor emission continued from subsidiary vents. No casualties or damage were reported.

The Ardoukoba (Asal) Rift in Djibouti (figure 1), trending NW from the Red Sea, contains a broad area of youthful fissure vents between Lake Asal and the Ghoubbat al Kharab gulf. Although no previous eruptions have been reported in the area in historic time, the most recent lava flows are substantially younger than sediments ¹⁴C dated at 5,300 B.P., and are thought to be younger than 3,000 B.P. Eruptions are also mentioned in local legends (Delibrias and others, 1975).

Figure 1. Map of the Ardoukoba Rift area (left), indicated by index map (right), showing rock types and volcanic centers. Latitudes and longitudes were added by SEAN and are approximate. Both maps after Delibrias and others (1975).

Reference. Delibrias, G., Marinelli, G., and Stieltjes, L., 1975, Spreading rate of the Asal Rift, in Pilger, A. and Rosler, A. (eds.), Afar Depression of Ethiopia: Inter-Union Commission on Geodynamics Scientific Report No. 14: E. Schweitzerbart'sche Verlagsbuchhandlung, Stuttgart.

Information Contacts: W. Clarke, U.S. Embassy, Djibouti; M. Krafft, Cernay, France; USGS/NEIC.

December 1978 (SEAN 03:12) Cite this Report

New data on November eruption

The eruption of Ardoukoba began on 7 November. During the preceding 24 hours, about 800 earthquakes M < 3.3 had been recorded. These events occurred at the end of the Ghoubbat al Kharab (figure 2), just S of the rift and ~6 km SE of the eruption site.

Figure 2. Rock types, faults, and old volcanic cones in the Ardoukoba Rift, after Needham and others (1976). An overprint, from M. Krafft, shows the active vents and lava flows from the 7-14 November 1978 eruption and the zone of active faulting accompanying the eruption.

After a brief period of gas emission, lava fountaining began from a 500-m-long, newly opened fissure. Three spatter cones formed on this fissure, but the primary activity soon shifted about 1/2 km to the SE. For the first 2-4 hours as much as 0.5 x 10⁶ m³ of lava was extruded per hour, but the extrusion rate declined rapidly and by the 5th or 6th day had decreased by an order of magnitude.

By 9 November, only the main vent was still active. A cone (named Gira-le-Koma) about 30 m high, 200 m long, and 25 m wide, with a 60° external slope, had formed around this vent, which contained a small lava lake. On 13 November the level of the lava lake dropped rapidly, then the lake disappeared. Scoria and bombs were ejected briefly before the eruption ended on 14 November.

The total volume of lava emitted was estimated to be at least 12 x 10⁶ m³. Lava covered an area of slightly more than 3 km². Flow thicknesses reached 25 m but usually ranged from 1 to 2 m. About 25 fissures, parallel to the NW-SE trend of the rift, opened during the activity. Most fissures were from 1-2 mm to about 1 m wide, but there was one short segment of 3 m width. Many of the fissures also showed a component of normal movement, with scarps up to 1/2 m high.

Reference. Needham and others, 1976, The accreting plate boundary: Ardoukoba Rift (northeast Africa) and the oceanic rift system: Earth and Planetary Science Letters, v. 28, p 439-453.

Further References. Abdallah, A., and others, 1979, Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries: Nature, v. 282, p. 17-23.

Demange, J., and Tazieff, H., 1978, The "tectonic" eruption of the Ardoukoba (Djibouti): C.R. Acad. Sci. Paris, Ser. D, v. 287, p. 1269-1272.

Hernandez, J., and Ruegg, J.C., eds., 1980, Colloque Rift d'Asal: Réunion extraordinaire de la Société Géologique de France: Bulletin de la Societé Géologique de France, serie 7, t. XXII, no. 6, p. 797-1013.

Tarantola, A., Ruegg, J.C., and Lepine, J.C., 1979, Geodetic evidence for rifting in Afar: A brittle-elastic model for the behavior of the lithosphere: Earth and Planetary Science Letters, v. 45, p. 435-444.

Information Contacts: M. Krafft, Cernay.